Method for enhancing sludge conditioning effect by coupling ozone with perborate

Abstract

A method for enhancing sludge conditioning effect of ozone coupled with perborate is provided. The method comprises: step 1: providing residual sludge of municipal wastewater treatment plant, perborate, ozone and flocculant; step 2: adding perborate to the residual sludge; step 3: introducing ozone into the residual sludge; step 4: after completion of step 3, adding flocculant and uniformly stirring, and then standing. Step 5: filtering the product obtained by step 4.

Description

Technical Field

[0001] This application belongs to the field of environmental engineering technology and relates to the chemical conditioning of sludge to improve sludge dewatering performance, reduce the moisture content of dewatered sludge cake (<60%), achieve the effect of deep sludge dewatering, and promote the resource reuse of sludge after dewatering. Background Technology

[0002] The residual sludge produced by urban wastewater treatment plants has a complex composition, containing a large number of harmful components such as parasite eggs, pathogens, organic debris, and heavy metals. It is also prone to decay and foul odors, leading to a decline in environmental quality and posing potential threats to public health. Sludge reduction and harmless treatment are important issues and major challenges currently facing wastewater treatment plants.

[0003] Sludge contains 50-80% organic matter, mainly biopolymers such as polysaccharides, proteins, humic acids, and nucleic acids. These organic compounds carry negative charges and maintain the stability of the biocolloids through electrostatic repulsion. Due to their highly hydrophilic chemical groups, a large amount of water is bound within the sludge's colloidal network structure. The sludge particles are extremely small, with a median particle size (D50) typically between 30-60 μm, resulting in a very large specific surface area and consequently, a high adsorbed water content. These factors contribute to the sludge's high compressibility, high filtration impedance, and poor dewatering performance. While traditional coagulation / flocculation combined with mechanical dewatering can remove some water from the sludge, the final dewatered sludge cake still has a moisture content as high as 75-85%, which is insufficient to meet the moisture content requirements of relevant national standards for subsequent sludge landfilling, composting, and land application. Therefore, to improve the removal of bound water from the sludge, it is necessary to condition the sludge before dewatering.

[0004] Currently, sludge conditioning methods mainly include thermal treatment, ultrasonication, freeze-thaw cycles, chemical treatment, and bioleaching. In recent years, chemical conditioning methods, in particular, have gained widespread attention due to their rapid and efficient characteristics. Compared to other chemical agents, ozone has advantages such as being environmentally friendly, cost-effective, requiring little space, and easy to operate, and has been widely used in wastewater treatment. However, after ozone oxidation, sludge exhibits a surge in extracellular polymers and a decrease in sludge zeta potential, leading to a deterioration in sludge dewatering performance. This is mainly attributed to the selective nature of direct ozone oxidation and its relatively weak oxidizing capacity (E0 = 2.07V), which cannot completely oxidize and decompose organic matter with negatively charged extracellular groups. By enhancing ozone decomposition, active oxygen, primarily hydroxyl radicals (E0 = 2.87V), is generated, which indiscriminately oxidizes the vast majority of organic matter. This undoubtedly greatly helps reduce extracellular polymers in sludge, increase the sludge zeta potential, and is expected to improve sludge dewatering performance.

[0005] Therefore, there is an urgent need to develop a novel ozone oxidation conditioning process to enhance the degradation of extracellular hydrophilic organic matter, promote the release of bound water from sludge, and improve the dewatering performance of sludge. Simultaneously, the rationality of the selection of chemicals should also be considered to promote the resource-based reuse of dewatered sludge. Summary of the Invention

[0006] To improve the dewatering performance of sludge and promote its resource recycling, the inventors conducted in-depth and extensive research. They unexpectedly discovered that adding perborate to the sludge and then introducing ozone, followed by treatment with a flocculant, significantly improves the sludge dewatering efficiency. Based on this, this application provides a novel sludge conditioning method.

[0007] This application provides a method for conditioning sludge, the method including:

[0008] Step 1: Provide residual sludge from the municipal wastewater treatment plant, perborate, ozone, and flocculants;

[0009] Step 2: Add perborate to the remaining sludge;

[0010] Step 3: Introduce ozone into the remaining sludge;

[0011] Step 4: After completing step 3, add flocculant and stir evenly, then let stand;

[0012] Step 5: Filter the product obtained in step 4.

[0013] In one embodiment, the amount of perborate is 20-180 mg / g, preferably 40-140 mg / g, and more preferably 60-100 mg / g, based on the dry matter weight% of the residual sludge.

[0014] In one embodiment, the perborate may be selected from any one or a combination of calcium perborate or sodium perborate.

[0015] In one embodiment, the ozone intake flow rate in step 3 can be 0.5-1.5 L / min, preferably 0.8-1.3 L / min, and more preferably 1.0-1.2 L / min.

[0016] In one embodiment, the concentration of ozone in step 3 can be 20-120 mg / L, preferably 30-80 mg / L, more preferably 40-80 mg / L, and even more preferably 40-60 mg / L.

[0017] In one implementation, step 2 is performed after step 3 is completed. In another implementation, steps 2 and 3 are performed simultaneously.

[0018] In one implementation, the amount of flocculant may be 1-5% based on the dry matter weight percentage of the residual sludge.

[0019] In one embodiment, the method further includes: after completing step 3 and before proceeding to step 4, preparing the flocculant into an aqueous solution with a mass fraction of 1-10%, preferably 3-5%.

[0020] In one embodiment, the flocculant may be selected from any one or a combination of polyaluminum ferric silicate, polyaluminum chloride, polyferric sulfate, ferric sulfate, or aluminum chloride.

[0021] In one embodiment, the filtration in step 5 can be performed by atmospheric pressure filtration, pressurized filtration, or depressurized filtration.

[0022] In one embodiment, the filtration is performed by passing the product obtained from step 4 through a 100-800 mesh sieve.

[0023] In one embodiment, the method further includes drying the filter residue after filtration in step 5.

[0024] In one embodiment, the drying is selected from low-temperature drying, room-temperature drying, high-temperature drying, or a combination thereof. Detailed Implementation

[0025] The "range" disclosed in this document is represented in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive of endpoints and can be combined with each other; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0026] In this application, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is simply a shortened representation of these numerical combinations.

[0027] In this application, the words "above" or "below" following a number include the number itself. For example, "below 5" means less than or equal to 5, and "above 7" means greater than or equal to 7.

[0028] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0029] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0030] In this application, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0031] In this application, unless otherwise specified, the term "comprising" as used herein can be either open-ended or closed-ended. For example, "comprising" may mean that it may also include other components not listed, or it may only include the listed components.

[0032] The above description is also the conventional expression method used in this field. It should be emphasized that the following descriptions are merely some specific embodiments of the present invention, and the scope of protection of the present invention is not limited to these specific embodiments. The scope of protection of the present invention is defined by the claims of the present invention, and may include any technical means within the scope of the claims, including but not limited to further improvements and substitutions to these specific embodiments.

[0033] The method described in this application will now be explained in detail.

[0034] In one embodiment, the present invention provides a method for conditioning sludge, the method comprising the following steps 1-4:

[0035] Step 1: Provide residual sludge from the municipal wastewater treatment plant, perborate, ozone, and flocculant.

[0036] This application does not restrict the source of the residual sludge. For example, the sludge may come from industrial wastewater or domestic sewage treatment.

[0037] Step 2: Add perborate to the remaining sludge.

[0038] Perborate refers to salts containing BO3. -The salt can be hydrated or non-hydrated. When perborate is added to the excess sludge, it releases hydrogen peroxide, which reacts with ozone in step 3 below to form reactive oxides. These reactive oxides then disrupt sludge flocs and bacterial cell membranes, thereby releasing bound water and intracellular water.

[0039] In embodiments of this application, the perborate may be selected from calcium perborate, sodium perborate, their hydrates, or combinations thereof. In one embodiment, the perborate is calcium perborate. In another embodiment, the perborate is sodium perborate. Preferably, the perborate is calcium perborate.

[0040] In one implementation, step 2 can be performed first, followed by step 3, which is detailed below. In another implementation, step 2 and step 3, detailed below, can be performed simultaneously, i.e., ozone is introduced while perborate is added.

[0041] In embodiments of this application, the amount of perborate, based on the dry matter weight percentage of the residual sludge, is 20-180 mg / g. For example, 30 mg / g, 40 mg / g, 50 mg / g, 60 mg / g, 70 mg / g, 80 mg / g, 90 mg / g, 100 mg / g, 110 mg / g, 120 mg / g, 130 mg / g, 140 mg / g, 150 mg / g, 160 mg / g, or 170 mg / g.

[0042] To determine the dry matter weight of the residual sludge, a small sample of residual sludge (e.g., 1 gram) can be dried at 103-105℃ for 2 hours to obtain completely dried dry matter. This determines the proportion of dry matter in the residual sludge, and then the dry matter weight of the residual sludge used can be determined by conversion.

[0043] Step 3: Introduce ozone into the remaining sludge.

[0044] In this step, ozone is introduced into the remaining sludge, causing the hydrogen peroxide released from the perborate added in step 2 to couple with the ozone in step 3. Specifically, as described above, the perborate added to the remaining sludge in step 2 releases hydrogen peroxide, which reacts with the ozone in step 3 to form active oxides. These active oxides then disrupt the sludge flocs and bacterial cell membranes, thereby releasing bound water and intracellular water.

[0045] The following equation illustrates the process by which hydrogen peroxide reacts with ozone to form reactive oxides:

[0046] 2H₂O₂ + 2O₃ → H₂O + 3O₂ + HO₂ · +·OH

[0047] As mentioned above, step 3 can be performed after step 2 is completed. Alternatively, steps 2 and 3 can be performed simultaneously.

[0048] In this implementation, the ozone intake flow rate in step 3 can be approximately 0.5-1.5 L / min. For example, the ozone intake flow rate can be approximately 0.6 L / min, 0.7 L / min, 0.8 L / min, 0.9 L / min, 1.0 L / min, 1.1 L / min, 1.2 L / min, 1.3 L / min, or 1.4 L / min.

[0049] In this embodiment, the concentration of ozone is about 20-120 mg / L, for example, about 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L or 110 mg / L.

[0050] In this embodiment, ozone can be introduced at room temperature (approximately 25°C). In this embodiment, the inlet pressure containing ozone can be 0.095 MPa, with a permissible fluctuation of 5%.

[0051] Step 4: After completing step 3, add flocculant and stir evenly, then let stand.

[0052] In this implementation, after step 3 is completed, the ozone supply is stopped. Then, a flocculant is added to the product of step 3.

[0053] The flocculant causes the product of step 3 to flocculate, thereby further increasing the dewatering efficiency of the conditioned sludge.

[0054] In this embodiment, the flocculant may be selected from any one or a combination of polyaluminum ferric silicate, polyaluminum chloride, polyferric sulfate, ferric sulfate, or aluminum chloride. In one embodiment, the flocculant may be polyaluminum ferric silicate. In another embodiment, the flocculant may be polyaluminum chloride. In yet another embodiment, the flocculant may be polyferric sulfate.

[0055] Preferably, the flocculant is polyaluminum ferric silicate. In particular, the advantages of using polyaluminum ferric silicate are at least as follows: silicate ions can combine with calcium and magnesium in sludge to form insoluble calcium silicate and magnesium silicate, which can become new skeletal structures after sludge decomposition; the reacted sludge flocs integrate the advantages of dense aluminum ion hydroxyl complex flocs and large iron ion hydroxyl complex flocs, which are beneficial for sludge filtration (e.g., pressure filtration) and dewatering.

[0056] In this implementation, the amount of flocculant may be 1-5%, for example 2%, 3% or 4%, based on the dry matter weight percentage of the residual sludge.

[0057] In this embodiment, a flocculant, such as polyaluminum ferric silicate, can be directly added to the product of step 3 to proceed to step 4. Alternatively, after completing step 3 and before proceeding to step 4, the flocculant can be prepared into an aqueous solution with a mass fraction of approximately 1-10%, and then this aqueous solution can be added to the product of step 3 to proceed to step 4. The mass fraction of the flocculant in the aforementioned aqueous solution can also be approximately 2%, 3%, 4%, 5%, 6%, 7%, 8%, or 9%.

[0058] After adding and stirring the flocculant, allow it to stand for a period of time to allow the solids to settle completely. The standing time depends on factors such as the perborate, flocculant, sludge composition, and temperature. For example, it can be left to stand for 0.5-2 hours.

[0059] After completing the steps in the above sludge conditioning process, the product can be filtered in step 5.

[0060] In this embodiment, the filtration in step 5 can be performed by atmospheric pressure filtration, pressurized filtration, or depressurized filtration. In one embodiment, the filtration is atmospheric pressure filtration. In another embodiment, the filtration is pressurized filtration. In yet another embodiment, the filtration is depressurized filtration.

[0061] In this embodiment, the filtration is performed by passing the product obtained from step 4 through a 100-800 mesh sieve, for example, through a 200 mesh or 400 mesh sieve.

[0062] The sludge conditioning method of this application can significantly reduce the water retention rate of the filtered sludge, for example, its moisture content can be as low as 45-60%, which is significantly lower than the 75-80% moisture content currently achievable in the art.

[0063] Optionally, after completing step 5, the filter residue can be dried. Those skilled in the art will understand that this drying can be carried out at low temperature, ambient temperature, or high temperature.

[0064] Compared with the prior art, this application has the following beneficial effects:

[0065] 1) This application significantly improves the dewatering performance of sludge by using perborate, ozone and flocculant in combination.

[0066] 2) Because the perborate used is slightly soluble in water, it can slowly release hydrogen peroxide. In contrast, if hydrogen peroxide is used directly, it easily leads to the interaction between the oxidant and reactive oxygen free radicals, greatly reducing the efficiency of degrading sludge organic matter and resulting in waste. Furthermore, the pH of perborate solution is alkaline. Under alkaline conditions, ozone molecules easily decompose to generate hydroxyl free radicals with higher potentials, while hydrogen peroxide aqueous solution is acidic, which is not conducive to the decomposition of ozone to generate free radicals. In addition, the introduced calcium ions (if calcium perborate is used) can bind to the active sites on sludge polysaccharides and proteins, improving sludge flocculation and dewatering performance, while boron is an element required for plant growth, which can make up for the deficiency in sludge and facilitate the subsequent land resource utilization of sludge.

[0067] 3) When flocculants that generate silicate ions are used, the silicate ions can combine with calcium and magnesium in the sludge to form insoluble calcium silicate and magnesium silicate, which can become new skeletal structures after the sludge is broken down. Moreover, calcium silicate and magnesium silicate are also excellent fertilizers, which are beneficial for subsequent resource utilization.

[0068] 4) The conditioned sludge flocs combine the advantages of dense aluminum ion hydroxyl complex flocs and large iron ion hydroxyl complex flocs, which are beneficial for sludge dewatering by pressure filtration.

[0069] Example

[0070] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0071] In the following embodiments, the sludge was taken from the Qingpu Wastewater Treatment Plant in Shanghai, with a moisture content >99%. After gravity settling for 24-48 hours, the moisture content of the sludge decreased to 97%, with an allowable deviation of 0.5%. The gravity-set sludge was then conditioned. After conditioning, a plate and frame filter press was used to filter the sludge at a pressure of 1 MPa for 30 minutes.

[0072] Example 1: Conditioning sludge using calcium perborate, ozone, and polyaluminum ferric silicate.

[0073] At room temperature, 2340 mg of calcium perborate was added to 1000 g of sludge with a moisture content of 97.1% and thoroughly mixed. Ozone at a flow rate of 1.0 L / min and a concentration of 50 mg / L was then introduced for 90 minutes. Afterward, 20 mL of polyaluminum ferric silicate (5%) was added and thoroughly mixed, and then allowed to stand overnight at room temperature.

[0074] The above product was filtered using a plate and frame filter press to obtain dewatered cake. According to the gravimetric method in CJ / T 221, the moisture content of the obtained cake was 46.5%.

[0075] Example 2:

[0076] Sodium perborate, ozone, and polyaluminum ferric silicate were used to condition the sludge.

[0077] At room temperature, 2500 mg of sodium perborate was added to 1000 g of sludge with a moisture content of 96.8% and thoroughly mixed. Ozone at a flow rate of 1.0 L / min and a concentration of 40 mg / L was then introduced for 120 minutes. Afterward, 25 mL of 5% polyaluminum ferric silicate was added and thoroughly mixed, then allowed to stand overnight at room temperature.

[0078] The above product was filtered using a plate and frame filter press to obtain dewatered cake. According to the gravimetric method (CJ / T221), the moisture content of the obtained cake was 50.3%.

[0079] Comparative Example 1: Sludge Dewatering Using Ozone Alone

[0080] At room temperature, ozone at a flow rate of 1.0 L / min and a concentration of 50 mg / L was subsequently introduced into 1000 g of sludge with a moisture content of 97.1% for 90 minutes. The sludge was then left to stand overnight at room temperature.

[0081] The above product was filtered using a plate and frame filter press to obtain dewatered cake. According to the gravimetric method (CJ / T221), the moisture content of the obtained cake was 87.5%.

[0082] Comparative Example 2: Sludge dewatering using polyaluminum ferric silicate alone

[0083] At room temperature, 25 mL of polyaluminum ferric silicate (5%) was added to 1000 g of sludge with a moisture content of 96.8% and stirred thoroughly. The mixture was then left to stand overnight at room temperature.

[0084] The above product was filtered using a plate and frame filter press to obtain dewatered cake. According to the gravimetric method (CJ / T221), the moisture content of the obtained cake was 75.3%.

[0085] Comparative Example 3: Using potassium permanganate, ozone, and polyaluminum ferric silicate to condition sludge

[0086] At room temperature, 2340 mg of potassium permanganate was added to 1000 g of sludge with a moisture content of 97.1% and thoroughly mixed. Ozone at a flow rate of 1.0 L / min and a concentration of 50 mg / L was then introduced for 90 minutes. Afterward, 20 mL of polyaluminum ferric silicate (5%) was added and thoroughly mixed, and then allowed to stand overnight at room temperature.

[0087] The above product was filtered using a plate and frame filter press to obtain dewatered cake. According to the gravimetric method (CJ / T221), the moisture content of the obtained cake was 67.5%.

[0088] Comparative Example 4: Using hydrogen peroxide, ozone, and polyaluminum ferric silicate to condition sludge

[0089] At room temperature, 78 mL of 30% hydrogen peroxide was added to 1000 g of sludge with a moisture content of 97.1% within 1 minute, and the mixture was stirred thoroughly. Then, ozone at a flow rate of 1.0 L / min and a concentration of 50 mg / L was introduced for 90 minutes. Afterward, 20 mL of 5% polyaluminum ferric silicate was added and stirred thoroughly, and then the mixture was allowed to stand overnight at room temperature.

[0090] The above product was filtered using a plate and frame filter press to obtain dewatered cake. According to the gravimetric method (CJ / T221), the moisture content of the obtained cake was 61.2%.

[0091] Comparative Example 5: Conditioning sludge using calcium perborate, ozone, and polyferric sulfate.

[0092] At room temperature, 2340 mg of calcium perborate was added to 1000 g of sludge with a moisture content of 97.1% and thoroughly mixed. Ozone at a flow rate of 1.0 L / min and a concentration of 50 mg / L was then introduced for 90 minutes. Afterward, 20 mL of polyferric sulfate (5%) was added and thoroughly mixed, and the mixture was allowed to stand overnight at room temperature.

[0093] The above product was filtered using a plate and frame filter press to obtain dewatered cake. According to the gravimetric method (CJ / T221), the moisture content of the obtained cake was 56.7%.

[0094] As can be seen from the above embodiments and comparative examples, compared with the comparative examples, the combination of perborate (e.g., sodium perborate, calcium perborate), ozone and flocculant (especially polyaluminum ferric silicate) used in this application to condition sludge significantly reduces the moisture content of the sludge cake, which means that the method of the present invention significantly improves the dewatering rate of sludge.

[0095] Although the claimed subject matter has been described according to various embodiments / implementations, those skilled in the art will recognize that various modifications / alterations, substitutions, deletions, and changes / variations can be made without departing from the spirit of the invention. Therefore, the scope of the claimed subject matter is intended to be defined solely by the scope of the appended claims, including their equivalents.

[0096] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for conditioning sludge, the method comprising: Step 1: Provide residual sludge from the municipal wastewater treatment plant, perborate, ozone, and flocculants; Step 2: Add perborate to the remaining sludge; Step 3: Introduce ozone into the remaining sludge; Step 4: After completing step 3, add flocculant and stir evenly, then let stand; Step 5: Filter the product obtained in step 4. in: The perborate is selected from calcium perborate. The flocculant is selected from polyaluminum ferric silicate, and The amount of perborate is 20-180 mg / g.

2. The method of claim 1, wherein, The amount of perborate is 40-140 mg / g, based on the dry matter weight percentage of the residual sludge.

3. The method of claim 1, wherein, The amount of perborate is 60-100 mg / g, based on the dry matter weight percentage of the residual sludge.

4. The method according to any one of claims 1-3, wherein, The ozone intake flow rate in step 3 is 0.5-1.5 L / min.

5. The method according to any one of claims 1-3, wherein, The ozone intake flow rate in step 3 is 0.8-1.3 L / min.

6. The method according to any one of claims 1-3, wherein, The ozone intake flow rate in step 3 is 1.0-1.2 L / min.

7. The method according to any one of claims 1-3, wherein, The ozone concentration in step 3 is 20-120 mg / L.

8. The method according to any one of claims 1-3, wherein, The ozone concentration in step 3 is 30-80 mg / L.

9. The method according to any one of claims 1-3, wherein, The ozone concentration in step 3 is 40-60 mg / L.

10. The method according to any one of claims 1-3, wherein, After step 2 is completed, proceed to step 3.

11. The method according to any one of claims 1-3, wherein, Steps 2 and 3 are performed simultaneously.

12. The method according to any one of claims 1-3, wherein, The amount of flocculant is 1-5% based on the dry matter weight percentage of the residual sludge.

13. The method according to any one of claims 1-3, wherein, After completing step 3 and before proceeding to step 4, prepare the flocculant into an aqueous solution with a mass fraction of 1-10%.

14. The method of claim 13, wherein, The flocculant is prepared as an aqueous solution with a mass fraction of 3-5%.

15. The method according to any one of claims 1-3, wherein, The filtration in step 5 is carried out by atmospheric pressure filtration, pressurized filtration, or depressurized filtration.

16. The method of claim 15, wherein, The filtration is performed by passing the product obtained from step 4 through a 100-800 mesh sieve.

17. The method according to any one of claims 1-3, wherein, The method further includes drying the filter residue after step 5.

18. The method of claim 17, wherein, The drying process is selected from low-temperature drying, room-temperature drying, high-temperature drying, or a combination thereof.